The storage capacity of visual short-term memory (VSTM) for simple objects is known to be severely restricted and to vary considerably across individuals. These individual differences in capacity have often been proposed to be due to variability in memory storage space. However, it is also possible that much of the variability stems from the efficiency of attentional control mechanisms that restrict access to VSTM. In previous experiments, we used a change detection task in which task-irrelevant objects (distractors) were also present to gauge how efficient individuals are at filtering out distractors from being encoded into memory system. By using an ERP index of the current number of objects held in VSTM, we have shown that the efficiency of excluding distractors from VSTM is strongly predicted by an individual's memory capacity. That is, low memory capacity individuals maintain more irrelevant items in VSTM than high capacity individuals. In the current series of experiments, we extend these results by parametrically varying the attributes of the distractors (i.e. similarity to target, exposure duration, and onset timing) to investigate what makes them more or less likely to be unnecessarily stored in VSTM and how these selection factors may be moderated by an individuals memory capacity.